i78 PRACTICAL ORGANIC CHEMISTRY salt. This is ascertained by filtering small samples and testing the filtrate with potassium carbonate. The liquid is ag-ain filtered through cloth or through a porcelain funnel and concen- trated first over a ring burner, and finally on the water-bath, until a sample crystallises on cooling. The potassium salt is drained at the pump and dried on porous plate. Yield, about 80 grams. CGHG + H2S04 = CGH5S03H + H2O. 2CGH5S03H + CaC03=(CcH3SOs)2Ca + C02 + H2O. (C0H6S03)3Ca+K2C03=2C6H5S03 Properties. — Colourless pearly plates, which slowly effloresce in the air and which melt above 300° with slight decomposition ; very soluble in water. See Appendix^ p. 292. PREPARATION 75. Benzenesnlphonic Chloride, C0H3SO2C1 Gerhardt, Chiozza, Annalen, 1853. 87, 299. 1 5 grms. potassium benzene sulphonate. 25 „ phosphorous pentachloride. The potassium benzenesulphonate is carefully dried on the water-bath, powdered, and mixed with the phosphorus penta- chloride in a flask.* A vigorous reaction sets in. When it has abated, the flask is heated on the water-bath for one hour,* and the mass occasionally stirred with a glass rod. The pro- duct is poured into a flask containing 200 c.c. cold water and allowed to stand an hour. The sulphonic chloride, which separates as an oil, is then extracted with ether, dehydrated over calcium chloride, decanted, and the ether removed on the water-bath. Yield, 10 grams of a light brown oil. Properties. — Colourless oil when pure ; b. p. 246 — 247° witli decomposition ; m. p. 14° ; distils undecomposed in vacua.